The present invention relates to a coating composition for a hard coat layer of a plastic lens, a process for the preparation thereof, and a scratch-resistant plastic lens. More specifically, the present invention relates to a coating composition which is applied to a plastic lens surface for lending scratch resistance, etc., thereto and which is formable into a hard coat layer excellent in adhesion, a process for the preparation thereof, and a plastic lens which has a hard coat layer made of the above coating composition formed on a surface thereof and is excellent in scratch resistance, and the like.
As compared with glass lenses, plastic lenses, allyldiglycolcarbonate resin lenses in particular, are light in weight and excellent in safety, processability and cosmetics, and are coming rapidly to be popular owing to developments of an anti-reflection techniques and hard coating techniques in recent years. Further, there are under way developments of lenses made of thermoplastic resins having a smaller molding time and a smaller molding shrinkage than thermosetting resins such as an allyldiglycolcarbonate resin. Particularly, a lens made of a polycarbonate resin has come to be popular due to its excellent impact resistance.
While plastic lenses are widely used as described above, the plastic lenses have a defect that they are easily scratched or marred as compared with glass lenses.
For overcoming the above defect, it is recent practice to coat a plastic lens surface with a material having a high hardness. For example, U.S. Pat. No. 3,986,997, U.S. Pat. No. 4,309,319 and U.S. Pat. No. 4,436,851 disclose an abrasion resistant coating composition formed of a mixture of an alkoxysilane with colloidal silica. A cured coating of the above coating composition has excellent adhesion to an acrylic resin substrate. However, it does not at all adhere to some other plastic substrates, or it peels off due to a change with the passage of time even if it has excellent adhesion in the beginning.
For application to a plastic such as a polycarbonate, which is poor in adhesion to an organosiloxane-containing hard coating agent, it is general practice to use a primer. The use of the primer causes problems in productivity that a coating machine or equipment is complicated and that the step of coating takes a longer time period, so that there has been desired a direct application method that can be carried out without any treatment with a primer.
As a method of direct application to a polycarbonate without any treatment with a primer, several methods have been proposed in JP-A-7-90224, and the like. In these methods, however, dyeing which is characteristic of a plastic lens is almost impossible. Further, when a general dipping method is employed for the application, interference fringes are caused by a difference between the refractive index of a polycarbonate and that of a hard coating film, which is undesirable in view of an appearance.
It is an object of the present invention to provide a coating composition for a hard coat layer, which coating composition overcomes the above defects of the prior art and can form a scratch-resistant hard coat layer having excellent adhesion to plastic lenses such as a Polycarbonate lens without using any primer, and having transparency and excellent dyeability, by a general application method, and a method of preparation thereof. It is also an object of the present invention to provide a scratch-resistant plastic lens having a coating formed by applying the above coating composition.
For achieving the above objects, the present inventor has made diligent studies and as a result has found that a composition containing, as essential components, a hydrolyzate of an organosilicon compound having a specific structure, specific metal oxide fine particles, a polyurethane and a curing agent can give a hard coat layer which not only has sufficient adhesion, dyeability and flexibility but also has excellent scratch resistance (abrasion resistance) when applied onto a plastic lens surface and cured under heat. On the basis of the above finding, the present invention has been completed.
That is, according to the present invention, there is provided a coating composition for a hard coat layer of a plastic lens, which comprises, as essential components, (A) a hydrolyzate of an organosilicon compound of the general formula (I), 
wherein R1 is an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 10 carbon atoms or a monovalent organic group having a mercapto group, an amino group, a methacryloxy group or an epoxy group, R2 is an alkyl group having 1 to 4 carbon atoms, R3 is an alkyl group having 1 to 10 carbon atoms, an alkoxyalkyl group having 2 to 10 carbon atoms or an acyl group having 2 to 10 carbon atoms, n is 0 or 1 and a plurality of (OR3)s may be the same or different, (B) at least one kind of fine particles selected from fine particles of oxides of silicon, aluminum, tin, antimony, zirconium, tungsten and titanium and composite fine particles of at least two oxides of these, (C) a polyurethane and (D) a curing agent.
According to the present invention, further, there is provided a method of preparation of a coating composition for a hard coat layer of a plastic lens, which comprises mixing an organosilicon compound of the general formula (I) which is a precursor of the above component (A) with a polyurethane as the above component (C) optionally together with a solvent, hydrolyzing the organosilicon compound, thereby obtaining a homogeneous solution of a hydrolyzate of the organosilicon compound of the above general formula (I) as the above component (A) and the polyurethane as the component (C), and then adding the fine particles as the component (B) and the curing agent as the component (D).
According to the present invention, further, there is provided a scratch-resistant plastic lens having a hard coat layer formed of the above coating composition on a surface thereof.
In the coating composition of the present invention, a hydrolyzate of an organosilicon compound of the general formula (I) is used as component (A). 
In the above general formula (I), R1 is an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 10 carbon atoms or a monovalent organic group having a mercapto, amino, methacryloxy or epoxy group. The above alkyl group, alkoxy group and alkenyl group may be linear, branched or cyclic. Examples of the alkyl group having 1 to 10 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, octyl, cyclopentyl and cyclohexyl groups. Examples of the alkenyl group having 2 to 10 carbon atoms include vinyl, allyl, propenyl, butenyl and hexenyl groups. Examples of the alkoxy group having 1 to 10 carbon atoms include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentoxy, hexoxy, octoxy, cyclopentoxy and cyclohexoxy groups. Examples of the aryl group having 6 to 10 carbon atoms include phenyl, tolyl, xylyl and naphthyl groups. Examples of the aralkyl group having 7 to 10 carbon atoms include benzyl and phenetyl groups. Further, the monovalent organic group having a mercapto, amino, methacryloxy or epoxy group is preferably an alkyl group having 1 to 6 carbon atoms and having the above substituent, and specific examples thereof include xcex3-mercaptopropyl, xcex3-aminopropyl, xcex3-methacryloxypropyl, xcex3-glycidoxypropyl and 3,4-epoxycyclohexyl groups.
R2 is an alkyl group having 1 to 4 carbon atoms, and the alkyl group may be linear or branched. Examples thereof include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl groups. R3 is an alkyl group having 1 to 10 carbon atoms, an alkoxyalkyl group having 2 to 10 carbon atoms or an acyl group having 2 to 10 carbon atoms. The alkyl group having 1 to 10 carbon atoms includes those explained with regard to the above R1. Examples of the alkoxyalkyl group having 2 to 10 carbon atoms include methoxymethyl, methoxyethyl, methoxypropyl, ethoxymethyl, ethoxyethyl and ethoxypropyl groups. Examples of the acyl group having 2 to 10 carbon atoms include acetyl, propionyl and butylyl groups. n is 0 or 1, and a plurality of (OR3)s may be the same or different.
Examples of the organosilicon compound of the above general formula (I) include methyltrimethoxysilane, ethyltriethoxysilane, vinyltriethoxysilane, phenyltriethoxysilane, dimethyldimethoxysilane, phenylmethyldimethoxysilane, xcex3-glycidoxypropyltrimethoxysilane, xcex3-glycidoxypropylmethyldiethoxysilane, xcex2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, xcex3-methacryloxypropyltrimethoxysilane, N-xcex2-(aminoethyl)-xcex3-aminopropyltrimethoxysilane, xcex3-aminopropyltrimethoxysilane, xcex3-mercaptopropyltrimethoxysilane and orthoethylsilicate. These compounds may be used alone or in combination.
In the present invention, a hydrolyzate of the above organosilicon compound is used as component (A). The method for hydrolysis is not specially limited, and can be selected from known methods. For example, there is preferably employed a method in which the hydrolysis is carried out without any solvent or in a water-miscible organic solvent such as an alcohol in the presence of an inorganic acid such as hydrochloric acid or sulfuric acid.
In the coating composition of the present invention, as component (B), there is used at least one kind of fine particles of oxides of silicon, aluminum, tin, antimony, zirconium, tungsten and titanium and composite fine particles of at least two oxides of these. In the present specification, the latter term xe2x80x9ccomposite fine particlesxe2x80x9d includes a mixture of at least two kinds of oxide fine particles selected from the former xe2x80x9cfine particles of oxidesxe2x80x9d (for example, see JP-A-56-84729) and a product prepared by modifying a mixture of at least two kinds of oxide fine particles selected from the former xe2x80x9cfine particles of oxidesxe2x80x9d. It is advantageous to use the fine particles as component (B) in a colloidal state where the fine particles are uniformly dispersed in water or an organic solvent. Further, the fine particles preferably have an average diameter in the range of from 1 to 200 mxcexc, and are properly selected as required depending upon a purpose in use of the coating composition.
In the present invention, one kind of the above metal oxide fine particles may be used, or two or more kinds of the metal oxide fine particles may be used in combination.
In the coating composition of the present invention, the polyurethane as component (C) is not critical so long as it is a transparent liquid polyurethane. It can be selected from a one-part thermoplastic polyurethane, a two-part thermoplastic polyurethane and a thermosetting polyurethane. In view of weathering resistance, a non-yellowing polyurethane is preferred. Examples of the one-part thermoplastic polyurethane include a trade name xe2x80x9cCoatron KYU-1xe2x80x9d and a trade name xe2x80x9cSanprene SP-75xe2x80x9d (both supplied by Sanyo Kasei Kogyo K. K.). Concerning the two-part thermoplastic polyurethane, the polyol component includes polyesterpolyol and acrylpolyol, and the isocyanate component includes hexamethylenediisocyanate, xylylenediisocyanate, hydrogenated xylylenediisocyanate, 4,4xe2x80x2-methylenebisdicyclohexyldiisocyanate and isophoronediisocyanate. Such a polyurethane can be selected from those described in JP-A-61-114203, JP-A-51-119309, JP-A-3-269507, JP-B-5-48253, JP-A-5-93803, JP-A-3-109502 and JP-B-6-79084.
Generally, a polyurethane has poor compatibility with an organic silicon compound and a metal oxide sol.
Even if a polyurethane is added in a small amount, or even if a coating composition forms a homogeneous transparent solution, a transparent coating is not easily formed when the coating is formed by curing, since fogging or phase separation is liable to take place.
The present inventor has overcome the problem of the above fogging and phase separation of the coating by mixing the organosilicon compound of the general formula (I) which is a precursor of the above component (A) with the polyurethane as the component (C) optionally together with a solvent, hydrolyzing the organosilicon compound, thereby obtaining a solution of a hydrolyzate of the organosilicon compound of the general formula (I) as component (A) and the polyurethane as component (C), and then adding the fine particles as component (B) and a curing agent as component (D) to the solution.
In the coating composition of the present invention, examples of the curing agent as component (D) include various acids, bases, metal salts of organic acids, metal alkoxides and metal chelate compounds, and the curing agent can be properly selected as required.
Examples of the above acids include an organic carboxylic acid, chromic acid, hypochlorous acid, boric acid, perchloric acid, bromic acid, selenious acid, aluminic acid and carbonic acid. Examples of the bases include amines such as allylamine, ethylamine and pyridine, sodium hydroxide and ammonium hydroxide. Examples of the metal salts of organic acids include sodium acetate and potassium formate. Examples of the metal alkoxides include alkoxides of metals such as aluminum, zirconium, titanium and magnesium. Examples of the metal chelate compounds include aluminum acetyl acetonate.
Concerning amounts of the components of the coating composition of the present invention, the amount of the metal oxide fine particles as component (B) per 100 parts by weight of the hydrolyzate of the organosilicon compound as component (A) is generally in the range of from 1 to 200 parts by weight, preferably 10 to 100 parts by weight. When the amount of the above component (B) is less than 1 part by weight, a cured coating may have insufficient hardness. When it exceeds 200 parts by weight, gelation is caused. The amount of the polyurethane as component (C) is generally in the range of from 0.1 to 100 parts by weight, preferably 0.5 to 50 parts by weight. When the amount of the above component (C) is less than 0.1 part by weight, a cured coating may have insufficient adhesion to a substrate. When it exceeds 100 parts by weight, it is observed that the transparency of a cured coating tends to decrease. Further, the amount of the curing agent as component (D) is generally in the range of from 0.1 to 50 parts by weight, preferably 1 to 20 parts by weight. When the amount of the curing agent is less than 0.1 part by weight, curing may be insufficient. When it exceeds 50 parts by weight, gelation is caused.
The coating composition of the present invention is generally diluted with a solvent when used. The solvent is preferably a water-soluble or water-compatible organic solvent. Examples of the solvent preferably include alcohols such as methanol, ethanol, propanol, butanol, ethoxyethanol, butoxyethanol and methoxypropanol, and cellosolves such as monomethyl, monoethyl and monobutyl ethers of ethylene glycol and propylene glycol. These solvents may be used alone or in combination. The solvent is preferably selected as required by taking account of the type of the polyurethane to be used and the solvent resistance of a substrate of a plastic lens to which the coating composition is to be applied.
In addition to the above components (A) to (D), the coating composition of the present invention may contain various additives generally used in conventional coating compositions for plastic lenses, for example, a resin such as an epoxy resin, an ultraviolet absorbent, a photo-stabilizer such as a hindered-amine-containing photo-stabilizer, an antioxidant and a surfactant as required for improving the coating composition in various properties, so long as the physical properties of a cured coating are not impaired.
The plastic lens to which the coating composition of the present invention is applied is not specially limited. Examples of the plastic lens to which the coating composition of the present invention is applied include a lens made of polymethyl methacrylate, a lens made of a polycarbonate, a lens made of an aliphatic allyl carbonate, a lens made of an aromatic allyl carbonate and a lens made of a polythiourethane. Of these, it is advantageous to apply the coating composition of the present invention to a lens made of a polycarbonate such as a polycarbonate lens having poor adhesion to a general organosiloxane hard coating agent.
The scratch-resistant plastic lens of the present invention is formed of one of the above plastic lens and a hard coat layer formed of the above coating composition on the surface of the plastic lens.
The method of applying the above coating composition to the plastic lens surface is not specially limited, and it can be selected, for example, from general methods such as a dipping method, a spin coating method or a spraying method as required. In view of surface accuracy, a dipping method and a spin coating method are particularly preferred.
The coating composition applied onto the plastic lens surface is generally cured by drying with heated air or by irradiation with active energy rays. The curing is preferably carried out in hot air having a temperature of 50 to 200xc2x0 C., particularly preferably carried out in hot air having a temperature of 70 to 130xc2x0 C. The active energy rays include far infrared ray, etc., and in this case, thermal damage can be decreased to a lower level.
In the above manner, a hard coat layer having transparency and having excellent adhesion, dyeability and scratch resistance can be formed on the surface of a plastic lens, particularly a polycarbonate-based lens, by a general application method without using a primer. The hard coat layer has a thickness generally in the range of from 1 to 10 xcexcm, preferably 2 to 5 xcexcm.
Preferably, a difference between the refractive index of the hard coat layer and the refractive index of a lens substrate is adjusted, and when the refractive index difference is adjusted to approximately 0.03 or less, interference fringes caused by the refractive index difference can be prevented.
In the scratch-resistant plastic lens of the present invention, an anti-reflection film may be formed on the above hard coat layer as required. As an anti-reflection film, a known anti-reflection film, such as a single-structured anti-reflection film made of an inorganic oxide, an inorganic fluoride or an inorganic nitride or a multi-structured anti-reflection film made of these can be formed by a physical vapor deposition method (PVD method) such as a vacuum vapor deposition method, a sputtering method or an ion plating method or by a chemical vapor deposition method (CVD method).
Specific examples of components for constituting a low-refractivity layer and a high-refractivity layer of the anti-reflection film include silicon dioxide, silicon monoxide, zirconium oxide, tantalum oxide, yttrium oxide, aluminum oxide, titanium oxide, magnesium fluoride and silicon nitride (see, for example, JP-A-56-116003 and JP-A-2-262104). The anti-reflection film generally has a thickness in the range of from 0.1 to 1 xcexcm.
The anti-reflection film formed on the hard coat layer improves the plastic lens in anti-reflection performances. Further, a water-repellent film may be formed on the above anti-reflection film (see, for example, Japanese Patent 2561395).
In the present invention, the plastic lens before the hard coat layer is applied can be dyed, or the plastic lens after the hard coat layer is formed or the hard coat layer and the anti-reflection film are formed can be dyed. The dye for the dyeing preferably includes a disperse dye and a cationic dye, and a disperse dye is particularly preferred. While dyeing conditions such as a dye concentration, a dyeing temperature and a dipping time period can be set in broad ranges, the dye concentration per liter of water is preferably 0.01 wt % to 5 wt %, the dipping time period is 10 minutes to 6 hours (preferably 20 minutes to 3 hours), and the dyeing temperature is 60xc2x0 C. to 100xc2x0 C. (preferably 80xc2x0 C. to 90xc2x0 C.), in view of light-shielding capability and reproduction of dyeing.
The present invention will be explained further in detail with reference to Examples hereinafter, while the present invention shall not be limited by these Examples.
Plastic lenses having a hard coat layer each were measured for various properties according to the following methods.
(1) Scratch Resistance
The surface of a plastic lens was rubbed with a steel wool #0000 and visually inspected for a scratch state, and the observed scratch state was evaluated on the basis of the following ratings.
A . . . Almost no large scratch is formed even a plastic lens surface is rubbed intensely.
B . . . A large scratch is formed when a plastic lens surface is rubbed intensely.
C . . . A surface comes to be opaque when a plastic lens surface is rubbed intensely.
(2) Adhesion
A lens surface was cross-cut at intervals of approximately 1 mm, a cellophane tape (trade name xe2x80x9cCellotapexe2x80x9d, supplied by Nichiban K. K.) was intensely attached and then rapidly peeled off, and squares formed of a remaining coating on the lens surface were counted.
(3) Dyeability
Water was added to 3 ounces (approximately 85 g) of a disperse dye (Molecular Catalytic Brown, supplied by BPI), and the disperse dye was dispersed to prepare 1 liter of a dyeing bath. A plastic lens was dyed in the dyeing bath at 90xc2x0 C. for 10 minutes to evaluate the lens for dyeability.
(4) Appearance
A plastic lens was visually inspected under a fluorescent lamp in a dark room for defects on its appearance such as fogging.
(5) Refractive Index
Measured with an Abbe refratometer supplied by Atago.